Instantiating JSREPL

inputCallback: A callback function that is called when the language interpreter
is requesting input from the user. It will be passed a continuation callback that
should be called with the user input. Typically the interpreter would block until
input is received hence this is a mandatory callback.

outputCallback: An optional callback function that is called when the engine
has output to flush out to the standard out.

resultCallback: An optional callback function that is called when the interpreter
has successfully evaluated a program and passed the resulting evaluated value.

errorCallback: An optional callback function that is called if evaluatiing a
program yielded an error and passed the error.

progress: An optional callback function that is called repeatedly while loading
a language interpreter with the progress percentage.

timeout: Sets a timeout for running a program.

time: Milliseconds to wait.

callback: The callback function that is called when a program times out. This
callback must handle recovering the system (i.e. call jsrepl.loadLanguage etc.).
Must return true to stop the timeout from firing again.

API

JSREPL::loadLanguage

Loads a language interpreter. Takes three arguments:

stringlang_name: The name of the language to load.

functioncallback: Called when the language has been successfully loaded.

booleanworker_friendly (optional): By default JSRPEL would try to load
interpreters into Web Workers, this argument would force either loading in a
Worker (true) or loading in an iframe (false).

Example:

jsrepl.loadLanguage('python',function(){alert('Python loaded');});

JSRPEL::eval

Evaluates a program in the currently loaded language interpreter. Takes one argument:

stringcommand: The program string to evaluate.

Example:

jsrepl.eval('1+1');

JSREPL::getLangConfig

Returns the configuration object for a given language. Takes one argument:

stringlang_name: The language whose config will be returned. Defaults
to the current language name.

JSREPL::checkLineEnd

Given a command, decides whether it is ready for execution, as opposed to being
unfinished, such as missing a closing brace.

stringcommand: The program string.

functioncallback: The callback will be called with true if the command
is ready for execution, or false if it is incomplete.

JSREPL::on

Attaches a listener to one or more events. Takes two arguments:

string | arrayevent_type: Event(s) to listen to.

functioncallback: The function to call when the event is fired. Will
be called with whatever arguments the event supplies.

JSREPL::off

Detaches a listener or all listeners to one or more events. Arguments:

string | arrayevent_type: Event(s) to detach listener(s) from.

functionlistener: The listener function to detach. If not supplied then
all listeners will be detached.

JSREPL::once

Attaches a listener to one or more events that will only be called once.
Arguments:

string | arrayevent_type: Event(s) to listen to.

functioncallback: The function to call when the event is fired.

Events

input

Fired when the current language interpreter asks for input.
Arguments:

functioncallback: The program execution continuation callback.
Must be called with the string from the user input. Note that only
one input listener should call this callback.

output

Fired each time the current language interpreter has output to standard out.
Arguments:

stringdata: The output string.

result

Fired when the language interpreter has a result from the latest eval.
Arguments:

stringdata: The stringified result from the latest eval.

error

Fired when the language interpreter has an error from the latest eval.
Arguments:

stringerror: The stringified error from the latest eval.

progress

Fired when JSREPL has load progress percentage from loading a language
interpreter to report.
Arguments:

floatpercentage: How much of the interpreter file(s) was loaded.

timeout

If JSREPL was instantiated with the timeout option that includes the time
to wait on a running program before calling the specified callback (see
Instantiating JSREPL) and firing this event.

ready

Fired when a language is loaded and is ready to eval.

Standard input hacks

Problem

Language interpreters that are compiled with Emscripten expect input to be
to be a blocking call (synchronous). The only way to get blocking input
prompts in browsers is by using window.prompt. While suboptimal, it
works. However, that way we lose the ability to load interpreters in Web
Workers (because Workers have no access to dialog boxes).

Loading interpreters in workers has many benefits including not blocking
the main UI thread while the interpreter is intializing or working and the
ability to catch infinite loops (see timeout event). Despite these
advantages, until recently we avoided Workers in order to support input,
so we loaded languages which expect blocking input calls in an iframe
instead of a web worker. However in recent builds of Firefox and Chrome
that approach was broken for us because we could no longer do synchronous
binary XHRs, e.g. to read library files.

Solution

Webkit browsers

In WebKit-based browsers, we have leveraged the non-standard Web SQL Database
to share resources between the main thread and the worker thread, as they
provide a synchronization mechanism that can be accessed from both the main
page thread and from a worker. (See repl.coffee and sandbox.js).

Firefox

Unfortunately we couldn't do the same in Firefox, as it does not implement Web
SQL, and still does not support the standard IndexedDB Sync API. Instead, we
have used XHR to synchronously communicate between the worker and the main
thread using our server as a crude proxy. There is a sample server
implementation in the repl.it static server.

License

jsREPL is available under the MIT license. Language interpreters and the
modifications done to them by jsREPL developers have their own licenses, found
in their extern/{language} folders or submodules.